Set up Hydra server

[quantum9Innovation]

Due to the lack of an existing binary cache for the Humble distribution in nix-ros-overlay, we will need to provide an on-premises binary cache of the packages used in the Arcturus codebase. Setting up a Hydra server and uploading build artifacts from a job on that server to a Cachix instance seems to be the most reliable way to do this, but Cachix is an external tool and running a local binary cache may be better. For now, however, Cachix seems to be the easiest solution to integrate for flake consumers, so that leaves the automatic publishing of build artifacts to Cachix as the only task to be completed.